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Observations of Ship Tracks from Ship-Based Platforms JANUARY 1999 PORCH ET AL. 69 Observations of Ship Tracks from Ship-Based Platforms W. P ORCH,* R. BORYS,1 P. D URKEE,# R. GASPAROVIC,@ W. H OOPER,& E. HINDMAN,** AND K. NIELSEN# * Los Alamos National Laboratory, Los Alamos, New Mexico 1 Atmospheric Sciences Center, Desert Research Institute, Reno, Nevada # Department of Meteorology, Naval Postgraduate School, Monterey, California @ The Johns Hopkins University, APL, Laurel, Maryland & Naval Research Laboratory, Washington, D.C. ** Earth and Atmospheric Sciences Department, City College of New York, New York, New York (Manuscript received 17 October 1997, in ®nal form 17 February 1998) ABSTRACT Ship-based measurements in June 1994 provided information about ship-track clouds and associated atmo- spheric environment observed from below cloud levels that provide a perspective different from satellite and aircraft measurements. Surface measurements of latent and sensible heat ¯uxes, sea surface temperatures, and meteorological pro®les with free and tethered balloons provided necessary input conditions for models of ship- track formation and maintenance. Remote sensing measurements showed a coupling of ship plume dynamics and entrainment into overlaying clouds. Morphological and dynamic effects were observed on clouds unique to the ship tracks. These morphological changes included lower cloud bases early in the ship-track formation, evidence of raised cloud bases in more mature tracks, sometimes higher cloud tops, thin cloud-free regions paralleling the tracks, and often stronger radar returns. The ship-based lidar aerosol measurements revealed that ship plumes often interacted with the overlying clouds in an intermittent rather than continuous manner. These observations imply that more must be learned about ship-track dynamics before simple relations between cloud condensation nuclei and cloud brightness can be developed. 1. Introduction This is due to the subtle boundary layer cloud pertur- bations that may trigger ship tracks and the dif®culty Ship-track clouds were ®rst described by Conover in measuring these perturbations. The marine environ- (1966) as anomalous cloud lines observed in satellite ment associated with ship tracks represents extremes images. These cloud lines can extend for hundreds of with respect to low concentrations of cloud condensa- kilometers and persist for several days. Multiple obser- tion nuclei (CCN) and the lack of surface temperature vations made from a small research vessel (R/V Glorita) during the Monterey Area Ship Tracks (MAST) exper- and roughness differences associated with convective iment in June 1994 are combined to describe the phys- turbulence effects in clouds. Numerical models that go ical and dynamic characteristics of ship-track clouds. A beyond most plume rise and dispersion models can be wide variety of aerosol and meteorological parameters useful in understanding the sensitivity of marine strat- were simultaneously measured from the R/V Glorita iform clouds to CCN and turbulence effects. Innis et al. with aircraft ¯ights. The focus of the surface, airborne, (1998, manuscript submitted to J. Atmos. Sci.) calculate and satellite studies during MAST was to improve the that temperature differences as small as 0.18C can in- characterization of aerosol microphysical properties and crease cloud-level aerosol concentrations by over a fac- cloud dynamic processes in ship tracks (MAST 1994). tor of 2 in decoupled boundary layer conditions. Sys- Only a few studies of the in situ characteristics of tematic vertical velocities as low as a few centimeters ship tracks have been carried out. In studies to date, per second and/or associated air temperature increases emphasis has been on the aerosol microphysical char- of less than 1 K have produced modi®cations of marine acteristics of ship tracks (Ackerman et al. 1993; Al- boundary layer clouds in a statistical±dynamic numer- brecht et al. 1989; Radke et al. 1989; Ferek et al. 1998), ical model that mimic many of the morphological and while cloud dynamic aspects have been largely ignored. cloud liquid water characteristics associated with ship tracks (Porch et al. 1990). Important measurements were made during the MAST experiment from the R/V Glorita. Vertical pro- Corresponding author address: William M. Porch, Atmospheric ®les of background meteorological parameters (needed Physicist, D-407, Los Alamos National Laboratory, Los Alamos, NM 87545. as input to numerical models simulating ship tracks) E-mail: [email protected] were obtained from both rawinsonde and tethered bal- q 1999 American Meteorological Society Unauthenticated | Downloaded 10/02/21 06:02 PM UTC 70 JOURNAL OF APPLIED METEOROLOGY VOLUME 38 loons launched from the R/V Glorita (Syrett 1994). to about 500 m in the case of the USS Truxton and USS Also, surface properties such as sea surface tempera- Mount Vernon. Larger diesel ships within a few hundred tures and heat and moisture ¯uxes were obtained from kilometers of the USS Truxton and USS Mount Vernon measurements on the ship. Surface aerosol properties did make a visible ship track. More detailed information and lidar measurements of the interaction of ship plumes on these ships and their emissions is given by Hobbs and marine boundary layer clouds were made from the et al. (1998, manuscript submitted to J. Atmos. Sci.). ship (Hooper and James 1998, manuscript submitted to The instruments aboard the R/V Glorita consisted of J. Atmos. Sci.). Measurements of cloud bottom heights shipborne and balloon-borne sensors (Table 2). Ship- related to ship-track clouds were measured from the ship borne acoustic, optical, and microwave sensors probed with commercial ceilometers. the boundary layer far from the in¯uence of the ship Research vessel±based measurements of atmospheric and high surface winds. In situ shipborne measurement parameters associated with ship tracks have several ad- systems included a tower for measuring heat and water vantages over aircraft measurements, such as the re- vapor ¯uxes, coupled with a ¯oating sea surface tem- search vessel being stationed for long periods at sea. perature measuring device, plus visible and infrared ra- Consequently, data were obtained on the evolution of diometry operated by the NOAA Environmental Re- conditions leading to ship-track formation during the search Laboratories (ERL) (Fairall et al. 1997). The tow- day and at night. A ship-based experiment, called SEA- er was located near the bow of the ship and was about HUNT, was performed in 1991 off the coast of Southern 6 m above the deck (10 m above sea level) to avoid as California and northern Mexico to study ship tracks and much as possible the effect of the ship's air wake. The other external forcing on marine boundary layer clouds instrumentation included global positioning system (Hindman et al. 1994). This experiment documented the (GPS) position detection and mast motion sensors to ®rst surface observation of a ship-track cloud that was account for translation and rotation effects on the hor- known to be a ship-track cloud simultaneously observed izontal wind and vertical velocities needed for eddy cor- by satellite. relation and estimates of bulk heat and water vapor In this paper, we report on the in situ and remote ¯uxes. measurement system results aboard the R/V Glorita dur- In situ measurements of aerosol characteristics were ing the MAST experiment. Data from these sensors are made using a sampling on the ship's mast connected to combined to characterize the physical and dynamic instrumentation in a cabin 20 m below. In situ mea- structure of ambient and ship-affected clouds. surements of aerosol characteristics were made using a 5-cm-diameter sampling tube 6 m up the ship's mast connected to instrumentation in a cabin 14 m below. 2. Ship-based measurements during MAST The analysis of the aerosol sampled from the ship's mast The most important component of the ship-based included condensation nuclei (CN), CCN, spectra (Hud- measurements in MAST was the research ship and its son and Li 1995), and aerosol size distributions from deployment with respect to dedicated navy ships and diffusion battery measurements. A limited number (12) ships of opportunity that affected marine stratiform of aerosol ®lter samples were taken from a sampler at- clouds during MAST. A complete description of the tached to the ship's high mast. A nephelometer also was aircraft and ship operations, a description of the physical located on the mast. and power plants including the trajectory of each of the In situ balloon-borne sensors measured meteorolog- dedicated ships, and what is known about the ships of ical parameters. These included conventional tempera- opportunity can be found in Gasporivic (1995). In this ture, humidity, and wind pro®ling sensors for rawin- paper we will focus on the dedicated navy ships USS sonde and tethered balloons. Rawinsondes were Safeguard and USS Mt. Vernon; and on ships of op- launched every 3 h during potential ship track periods. portunity on 12, 27, and 28 June when ship tracks and Active remote sensing instruments included a scan- clouds that had been affected by ships that passed over ning lidar, which was mainly dedicated to studies of the research vessel. Figure 1 shows the ship tracks as ship plume and background aerosol inhomogeneities detected in the National Oceanic and Atmospheric Ad- and their transport and interaction with boundary layer ministration/Advanced Very High Resolution Radiom- clouds (Hooper and James 1998, manuscript submitted eter (NOAA/AVHRR) channel 3 satellite images for to J. Atmos. Sci.). Two commercial lidar±ceilometers these three days. An overview of information on the were mounted to the deck for continuous determination ships that produced many of the features in Fig. 1 are of cloud bottom heights and backscatter. The Pennsyl- given in Table 1. These ships varied in fuel type and vania State University (PSU) system was pointed ver- amount consumed from diesel, steam turbine, and nu- tically and the Los Alamos National Laboratory (LANL) clear.
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